1. Field of the Invention
The present invention is generally related to glass-pulling apparatus and methods, and is more specifically related to apparatus and methods for precision pulling of pipettes using a scanning laser.
2. Background
Various systems and methods for pulling pipettes are known in the art. Typically, they are used to reduce the diameter of a pipette by first softening a glass tube and then stretching it. For example, a pipette puller may start with a glass tube having an inside diameter of 1.0 mm and reduce the inner diameter at the tip of the pipette to a fraction of a micron. Glass micropipettes made in this manner are used in a myriad of scientific investigative techniques. Some uses of micropipettes are described in the inventor's prior U.S. Pat. No. 5,181,948, the disclosure of which is incorporated by reference. Various state-of-the-art commercial pipette pullers are available from Sutter Instrument Company, the assignee of the present invention; see, for example, the products listed at their website http://www.sutter.com.
Various heating techniques for softening the glass to be pulled are known in the art. In commercial embodiments, the glass tube (pipette) is typically heated using either a filament or a sufficiently high power laser, such as a CO2 laser. A pulling force is applied to the pipette which stretches to a reduced diameter. There are two main design approaches that are used to apply the necessary pulling force: (1) horizontal systems (i.e., where the central axis of the pipette is maintained in a horizontal orientation) must have two clamping mechanisms and typically rely on a solenoid or spring loaded mechanism to pull the heated glass, and (2) vertical systems, (i.e., where the central axis of the pipette is maintained in a vertical orientation) and rely simply on a weight attached to the bottom end of the glass tube to exert a preselected (depending on the weight) downward pulling force. Vertical systems may also clamp the glass at two positions and may used additional means for applying force. A simple vertical system with a pull supplied by a weight allows the glass to be easily rotated in order to produce a uniform heating around the glass. It is difficult to do this effectively with a horizontal configuration because the two separate glass clamps must be rotated synchronously and the clamping of the two sides must fall perfectly on a common line. If there is any offset or angle between the line of one clamp and the other that offset will reverse relative to the glass when the clamps rotate by 180 degrees. In cases where the glass has drawn down to a small diameter and a small length of glass is soft, this reversal will destroy the pipette even if the magnitude of the misalignment is quite small.
As noted, a pipette pulling system is typically used to form with very small diameter, thin-walled micropipettes. Because of the tiny size of the micropipettes that are produced, very small variations in the process parameters can have profound affects on the resultant product, sometimes in seemingly unpredictable ways. Accordingly, the user's selection of parameters to meet his or her specific needs is often as much art as science.
While pipette pullers have been available for decades, there is a continued need for pipette pulling systems and methods with greater precision, control and reproducibility.